An Internet protocol (IP) multimedia subsystem (IMS) is an architectural framework for transferring an IP multimedia service in various wired/wireless communication networks. In IMS, a protocol such as a session initiation protocol (SIP) applicable to various networks is used. SIP is a signaling protocol for controlling a multimedia service session through an IP and may be used to establish, correct and finish a unicast or multicast session. That is, IMS assists a user in easily accessing multimedia and audio data through various wired/wireless device(s).
Session(s) including one or more media flows (or media streams) may be configured through IMS. An IMS session may be expressed by a logical connection between a local side and a remote side via IMS network nodes. A counterpart user equipment (UE) or server of a local-side UE may be referred to as a remote end or remote party. That is, the remote end transmits and receives a media flow to and from the local-side UE via an IMS network.
A logical set of IMS sessions configured by a plurality of UEs may be referred to as a collaborative session. A controller UE controls a collaborative session and a controlled UE transmits and receives a media flow without collaborative session control rights. Collaborative session control may include collaborative session release, supplementary service call, inter-UE transfer (IUT) initiation, etc. IUT means that all or some of media flows and/or collaborative session control rights are transferred, replicated or shared between UEs.